An interesting topic, in addition to energy resources, production, and techno-economic analysis, could include sustainability life cycle assessment (SLCA). This is important because energy sustainability and sustainable development dominate round-table discussions worldwide.
One possible thesis topic for master's degree in energy economics could be: "The Impact of Renewable Energy Policies on Electricity Prices and Market Dynamics." This topic would involve analyzing how government policies promoting renewable energy sources such as wind and solar power affect electricity prices, market competition, and overall energy market dynamics. It could involve case studies of different countries or regions that have implemented renewable energy policies, as well as quantitative analysis of data on electricity prices and market trends. This topic is highly relevant in today's world as many countries are transitioning towards cleaner and more sustainable energy sources to combat climate change.
If the person is located in Europe, I recommend energy forecasting analysis and the factors that influence energy. This will equip the individual with knowledge of time series analysis, know about the power grid and prepare them for the future in this field.